The human-readable, service-specific universal ID used to represent the Persona.
This should be used whenever the user needs to be presented with a familiar, service-specific ID. For instance, in a prompt for the user to select a specific IM contact within an Individual to begin a chat with.
This is not guaranteed to be unique outside of the Persona's PersonaStore, but is guaranteed to be unique within it. If a suitable human-readable ID isn’t available from the backend, the display ID will be equal to the Persona.iid.